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Kinetic Modeling of Hydrothermal Aging of an Oxidation Catalyst with Wiremesh Structure as Part of the Motorcycle Emission Control System

Kouzehli, Ahmad | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57503 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Hamzehlouyan, Tayebeh; Khorasheh, Farhad
  7. Abstract:
  8. Diesel oxidation catalysts (DOCs) containing precious metals such as platinum and palladium are crucial components of the after-treatment system for exhaust gas purification in diesel vehicles and motorcycles. These catalysts aid in reducing the emission of pollutants into the environment by oxidizing carbon monoxide (CO) and hydrocarbons (HCs). However, their efficiency in removing environmental pollutants diminishes over time due to various deactivation mechanisms, especially by sintering. Given the significant contribution of motorcycles to CO and HC emissions, especially in least-developed countries, experimental and simulation studies on fresh and aged DOCs are essential for the optimal design of the after-treatment systems in motorcycles. In this venue, a kinetic model for a novel platinum and palladium-based motorcycle catalytic converter with wiremesh structure was developed in the present study using available experimental data. This model predicts the CO and propylene (as a representative of HCs) conversion trends over both fresh and hydrothermally aged catalysts under reducing and oxidizing atmospheres. The model incorporates the two-step oxidation phenomenon of CO caused by surface inhibitions from propylene-driven by-products like formate. Considering that the average diameter of the studied catalysts in the fresh state is 15.7 nm, which is above the critical structure-sensitivity threshold for reactions over platinum and palladium catalysts (6 nm and 10 nm, respectively), model optimization for aged samples was performed solely by adjusting the intrinsic rate constants. The results indicated that the exothermic nature of the reactions, especially C3H6 oxidation, significantly impacts the rate of the studied catalytic process. Therefore, based on the computational errors, non-isothermal modeling yields more reliable results (above 55%) compared to isothermal modeling. The non-isothermal steady-state kinetic model developed in this study accurately predicts the experimental light-off curves for the single and simultaneous oxidation of CO and propylene at various oxygen concentrations, from lambdas 0.6 to 1.2, using a single set of kinetic parameters. However, due to significant changes in activation energies when switching from fuel-rich to lean conditions, separate optimization of kinetic model parameters is recommended for better alignment with the intended operating conditions. Furthermore, based on the kinetic modeling results, a mathematical model was proposed to predict the aging trend of the catalyst as a function of the aging temperature. According to this model, oxidizing aging atmospheres at relatively lower temperatures lead to a greater reduction in catalytic activity compared to reducing atmospheres
  9. Keywords:
  10. Kinetics Modeling ; Oxidation Catalysts ; Catalyst Aging ; Motorcycle Oxidation Catalytic ; Wiremesh Structure ; Motorcycle Pollution

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